You hit it on the head, mopars are tough, and unleaded fuel in it self didn't cause any problems. But when you add the additional issue of tightening up emissions, all the manufacturers had trouble. Mopar just had less. except 440's and the slant six. They ran hot, and cracked heads because of the lean mixtures. Long stroke engines were doomed, as running efficiently was a pipe dream. The later 440 heads are great on 60's engines because they flow more coolant, but are thinner, which to me is Irrelevant as long as the smog controls are gone. and the 60's engines ran around 190 degrees, not 215 degrees like a 74' to 78' 440 model. if I were to build a 440, I would use the 73-78 440 head in the hot climates with TTi ceramic coated headers, then Overheating issues would be history.
